This invention relates to a novel method and apparatus for determining scale in photographic images.
The quality of a fabric, which can be used for items of clothing, upholstery, rugs, or carpets, is frequently associated with the closeness or fineness of a weave, or with the size of various features in the fabric such as tufts or knots. For example, conventional fabrics may be described in terms of the number of threads per inch, with a larger number usually designating a higher quality. The knot size and the density of knots present in the carpet can determine the relative quality of a carpet.
Accordingly, to evaluate fabric quality, it is desirable to be able to measure the fineness of weaves or other features. Various means of measurement have been employed, a common means being the use of a lens or magnifying glass, which is sometimes mounted on a support that includes a measuring scale. While such a method is useful with relatively light fabrics or swatches of fabric, it becomes impractical with heavier fabrics. It is particularly impractical, for example, when evaluating an oriental rug; not only is such a rug heavy, but also, no portion of the rug can be cut for sampling without destroying the rug.
There is a need, therefore, to provide a non-destructive, convenient means of measuring the fineness of a fabric such as an oriental rug.
The present invention allows a user to accurately judge the size of objects in a photograph. This invention was designed to facilitate both determining the knot size and calculating the knot density for a given section of carpet, thus determining the relative quality of the carpet. The main feature of the invention is a ruled frame, which is placed on a carpet. In a preferred configuration, the frame includes four sides, the interior edges of each side having indicia thereon corresponding to linear measurement scales. In this preferred embodiment, two diagonally opposite interior comers of the frame provide numerical origins for the scales. The frame can be sized to encompass the desired section of the carpet before it is photographed. Alternatively, the frame may be placed on the surface of the carpet, so that the resulting photograph gives the size of a particular feature, such as a knot, in the photograph.
The invention may also be used generally for determining the size of objects in photographs.
A preferred method of counting knots using the apparatus involves initially placing a section of carpet on a support surface. Then the ruled frame is placed over the carpet in view of the camera lens. The frame and the camera are configured so that the camera has a field of view that encompasses the frame. An image of the carpet and frame is then captured. This image may be transferred to a computer. When a user views an image captured by the camera, the indicia on the frame provide an instant reference against which the user can determine the size of features of the fabric without needing to know a relationship between the size of an object and the size of its image. The knot size is determined and the knots in the carpet are counted. The knot density can then be calculated. This process enables the viewer of the photograph to count the knots within a frame, without introducing scaling errors caused by enlargement or reduction.